1. Field of the Invention
The present invention relates generally to video communication systems and more specifically to a copy-protect video communication system. The present invention is particularly useful for standard digital television broadcasting.
2. Description of the Related Art
For standard digital television broadcasting, it is contemplated to multiplex text data with a video signal using vertical blanking intervals. For this purpose, a number of text data are multiplexed in a video program and each text data stream is associated with a particular series of video frames, or “events” so that each text appears on the screen of television receivers simultaneously with the associated event. In order for television receivers to synchronize a text data stream with the associated event, it is necessary for the broadcasting station to transmit timing information along with a video signal, as disclosed in Japanese Laid-Open Patent Application 11-27641. However, the use of timing information represents a waste of resource of the video frequency spectrum.
On the other hand, digital (or electronic) watermark is currently receiving attention because of its ability to detect illegal duplication of video programs and a number of techniques have been developed for hiding (embedding) identifying information into programs to be copy-protected.